Urbanization shapes the relation between density and melanin-based colouration in bird communities

<p>Growing urbanization increasingly influences ecosystems worldwide. While the effects of urban conditions within species (through either plastic or evolutionary responses) have been widely studied, their potential influences among species (through environmental filter), especially concerning their colouration, remain poorly known. Here, we investigated whether avian communities breeding inside and outside a major European city (Paris) differ with regards to melanin-based plumage colouration. Melanins are heritable pigments present in many taxa and have a series of unique properties that may allow coping with urban conditions. Using melanic-based colouration as an integrative phenotypic marker, we predicted (i) that the probability of breeding inside the city should increase with the intensity of species melanin-based colouration, (ii) that for species breeding both inside and outside the city, density should increase with the intensity of dark colouration inside the city, but not outside the city, and (iii) that species not breeding inside the city should not exhibit this positive relation between density and colouration. Our results confirmed these predictions. In addition, the density of species not breeding inside the city decreased with the darkness of their plumage. Altogether, these results suggest that bird species experience a balance between costs and benefits of melanin-based colouration shaped by environmental conditions. Both the environmental filtering and the urbanisation-shaped relation between density and colouration evidenced here are likely a general trend, however possibly modulated by additional local environmental conditions. Their importance may even be underestimated given the restricted geographical scale and the overall urbanization rate of the region studied. Further studies involving regions with contrasted environmental conditions should gain insight into the consequences of urbanization worldwide on traits associated with melanin-based colouration.</p>